[GreenKeys] final question on ST-6...

[Don Robert House]

Yep

I remember!

Don

On 21 Jul 2005, at 7:49 AM, wa2hwj at att.net wrote:

> Don't forget the TTY carrier equipment (43A) that used vacuum
>
> tubes. Talk about a heater! And, then there was the N-Carrier
>
> systems. Whenever I went into a CO, I would just walk
>
> down the hallway and feel the doors. When I felt a warm
>
> door, I knew it was the N-Carrier room! Lots of
>
> vacuum tubes in that stuff, too. (1970's)
>
>
> 73,
>
> Jack WA2HWJ
>
> -------------- Original message from Don Robert House  
> <drhouse at nadcomm.com>: --------------
>
>
> > Bill,
> >
> > Very sound and very accurate advice. In the Bell System we used very
> > similar rheostats to adjust loop currents, both in the central  
> office
> > and in the field. They were always attached to metal of one kind or
> > another. In the case of the Franklin Central Office in Chicago they
> > helped heat the building in both the winter and the summer ;-)
> > Some of the largest fans ran 24/7 trying the cool the area where all
> > of the telegraph circuits were "hubbed"
> >
> > I wish I had taken some photographs. I doubt many people would
> > believe what they were looking at.
> >
> > Best regards
> > and
> >
> > 73,
> >
> > Don
> > K9TTY
> >
> >
> > On 20 Jul 2005, at 10:15 AM, Bill Henry wrote:
> >
> > > Eugene,
> > >
> > > That is a 25 Watt, 2500 ohm rheostat on the back of your ST-6. It
> > > is supposed to get hot. The rear panel is a good heat sink, but
> > > don't touch the resistor! The loop supply of the ST-6 puts out
> > > about 150VDC @ 60 mA. With no machine in the loop, all of that
> > > power is dissipated in the loop pot. That rheostat normally
> > > dissipates about 9 Watts - and that is certainly enough to burn
> > > your finger. Plugging a machine into the loop will not reduce the
> > > heat dissipated by much as the machine's selector magnet DC
> > > resistance is only about 110 ohms, not much compared to the 2500
> > > ohm loop pot. But if you put several machines in series, the loop
> > > current will drop and you will then need to adjust the loop pot to
> > > get 60 mA. In practice, exact 60 mA is NOT critical - just try to
> > > get close (+/-10 mA).
> > >
> > > In regard to using a low voltage loop, that is not a good idea for
> > > older machines like the 15, 19, or most 28's. The selector magnet
> > > coils of a loop-driven TTY machine have a very high inductance -
> > > about 4 Hy as I recall. To assure that the magnet current rises
> > > quickly to a full 60 mA, you need to have a low L/R ratio to get a
> > > short time constant. That leads to a need for a high series
> > > resistance and that in turn to requiring a high voltage loop  
> supply
> > > to get 60 mA. The ST-6 has been around since the early 1970's and
> > > many of them have run continuously over that time. It's a proven
> > > design and works well. All of the ST-6's have a 25 Watt loop
> > > resistor. Only the early HAL ST-6's have the loop pot. This is a
> > > feature many hams actively look for. Hook up your Model 15 and
> > > have a good time.
> > >
> > > Bill Henry
> > >
> > >
> > > At 01:10 AM 7/20/2005 +0000, Eugene Hertz wrote:
> > >
> > >> Ok...
> > >>
> > >> The rheostat on the back of the ST-6 that controls the loop
> > >> current...
> > >>
> > >> 1. It gets VERY hot. REALLY hot! Is this normal? Is there any way
> > >> I could reduce the heat?
> > >>
> > >> 2. Seems like I can get the loop current to 60ma at the lowest  
> but
> > >> I can raise it to higher (not much) probably to compensate for
> > >> more devices on the loop..Question is, i would imagine my 28KSR
> > >> could probably work off lower voltage and/or current, no?
> > >>
> > >> Is there some way I could reduce the power consumed by the
> > >> rheostat, perhaps by reducing the current through it or voltage
> > >> across it? I recall some folks talking about running a loop on  
> 80v
> > >> instead of 100+v.
> > >> thanks
> > >> Eugene
> > >>
> > >>
> > >> _______________________________________________
> > >> GreenKeys mailing list
> > >> GreenKeys at mailman.qth.net
> > >> http://mailman.qth.net/mailman/listinfo/greenkeys
> > >>
> > >
> > >  
> ----------------------------------------------------------------------
> > > ----------------------
> > > George W. (Bill) Henry Internet: ghenry at halcomm.com
> > > President WWW: halcomm.com
> > > HAL Communications Corp. Phone: 217-367-7373
> > > 1201 W. Kenyon Rd. FAX: 217-367-1701
> > > Urbana, Illinois 61801
> > >  
> ----------------------------------------------------------------------
> > > ----------------------
> > >
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